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The centre of the globular cluster NGC 3201, as seen with the MUSE-instrument at the ESO-VLT. The arrow marks the star with the high velocity, which indicates the presence of a Black Hole. Credit: Sebastian Kamann and the MUSE collaboration

17 January 2018. Astronomers, under the lead of the Georg-August-Universität Göttingen and with participation of the Leibniz-Institut für Astrophysik Potsdam (AIP) using ESO’s MUSE instrument ...

Globular star clusters are huge spheres of tens of thousands of stars that orbit most galaxies. They are among the oldest known stellar systems in the Universe and date back to near the beginning of galaxy growth and evolution. More than 150 are currently known to belong to the Milky Way.

One particular cluster, called NGC 3201 and situated in the southern constellation of Vela (The Sails), has now been studied using the MUSE instrument on ESO’s Very Large Telescope in Chile. An international team of astronomers, led by the University Göttingen and with researchers from AIP, has found that one of the stars in NGC 3201 is being flung backwards and forwards at speeds of several hundred thousand kilometres per hour, with the pattern repeating every 167 days.

Lead author Benjamin Giesers (Georg-August-Universität Göttingen, Germany) was intrigued by the star’s behaviour: “It was orbiting something that was completely invisible, which had a mass more than four times the Sun — this could only be a black hole! The first one found in a globular cluster by directly observing its gravitational pull.”

The relationship between black holes and globular clusters is an important but mysterious one. Because of their large masses and great ages, these clusters are thought to have produced a large number of stellar-mass black holes — created as massive stars within them exploded and collapsed over the long lifetime of the cluster.

ESO’s MUSE instrument (developed and built by Göttingen and Potsdam, amongst others) provides astronomers with a unique ability to measure the motions of thousands of far away stars at the same time. With this new finding, the team has for the first time been able to detect an inactive black hole at the heart of a globular cluster — one that is not currently swallowing matter and is not surrounded by a glowing disc of gas. They could estimate the black hole’s mass through the movements of a star caught up in its enormous gravitational pull.

From its observed properties the star was determined to be about 0.8 times the mass of our Sun, and the mass of its mysterious counterpart was calculated at around 4.36 times the Sun’s mass — almost certainly a black hole.

Peter Weilbacher, one of the co-authors from AIP and in charge of the data reduction software for MUSE, is delighted: “A few years ago, the development of the detection methods started with a predecessor instument (PMAS) in Potsdam. With this discovery, the project has yielded a spectacular result.”

There is also an interesting historical connection to this discovery. “In 1915, Karl Schwarzschild was the first person to find a solution of the field equations of Einstein – at the time just a theoretical construct for what we call a black hole today. Also, Schwarzschild was head of the Göttingen observatory, before he became director at the Astrophysical Observatory Potsdam”, Martin Roth explains the historical connections between the German partner institutes.

The development of MUSE and the research about the globular clusters at Potsdam and Göttingen is supported by the BMBF Verbundforschung.

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

9 January 2018. The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first batch of high-spectral resolution data to ...

Spectral atlases are the fingerprints of stars and give insights into almost all of their physical properties like temperature, pressure, velocities and chemical composition. The first paper contains a new spectral atlas of the Sun and proves for the first time that a night-telescope instrument can reach a quality comparable to a specialized solar instrument. All solar and stellar spectra were taken with an unprecedented spectral resolution of λ/Δλ=250,000, a resolution equivalent to a 1/100th of the diameter of a hydrogen atom (λ being the wavelength and Δλ the smallest measurable separation of two wavelengths) and cover the entire optical and near-infrared light (from 383 to 914nm).

For the Sun several spectral time series with up to 300 individual spectra per day were pre-analyzed and are also provided to the community. "These data recover the well-known solar 5-minute oscillation at a peak of 3 mHz (5.5min) from the disk-averaged light with a radial-velocity amplitude of only 47 cm/s, an incredibly small velocity from a stellar point of view", says Prof. Strassmeier, PEPSI principal investigator and director of the Cosmic Magnetic Field branch at the Leibniz Institute for Astrophysics Potsdam (AIP). The new atlas was also used to re-determine the abundance of Lithium in the Sun with very high precision. "Lithium is a key element for the nucleosynthesis in the universe and is also a tracer of mixing processes inside stars", explains Dr. Matthias Steffen, one of the project scientists. Three-dimensional dynamic model atmospheres and a full statistical treatment of the spectral properties of the lithium atom were applied to determine the solar abundance.

The 48 stellar atlases in the second paper include the northern Gaia benchmark stars as well as other Morgan-Keenan standard stars. Spectra of these targets were not available at the given resolution and signal-to-noise ratio (S/N) before. The latter quantity represents the photon noise relative to the signal strength from the star and thus the quality of the spectra. Previously available S/N for work on astrophysical parameters was typically several hundred at a spectral resolution λ/Δλ of at most 100,000. "PEPSI and the LBT provide S/N of several thousand at on average three times higher spectral resolution", says Ilya Ilyin, PEPSI’s project scientist. "With such numbers we have now the typical daytime solar-like spectrum quality available also for bright stars at night time", adds Strassmeier.

Finally, in the third paper, the star "Kepler-444", hosting five sub-terrestrial planets, was confirmed to be 10.5 billion years old, more than twice the age of our Sun and just a little bit younger than the universe as a whole. The star is also found being poor on metals. The chemical abundance pattern from the PEPSI spectrum indicates an unusually small iron-core mass fraction of 24% for its planets if star and planets were formed together. For comparison, terrestrial planets in the solar system have typically a 30% iron-core mass fraction. “This indicates that planets around metal-poor host stars are less dense than rocky planets of comparable size around more metal-rich host stars like the Sun”, explains Claude “Trey” Mack, project scientist for the Kepler-444 observation.

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

29 November 2017. Astronomers using the MUSE instrument on ESO’s Very Large Telescope in Chile focused on the Hubble Ultra Deep Field, measuring distances and properties of 1600 very faint galaxi...

"The MUSE data enabled for the first time a systematic investigation of the motions of stars in galaxies in the early Universe. Our results show that regular stellar motions, typical of the star-forming galaxies in the present-day Universe, were already in place about 6 billion years ago,” explains Davor Krajnović, researcher at the Leibniz Institute for Astrophysics Potsdam (AIP) and one of the authors of the now published papers describing results from this survey.

The survey team observed a much-studied patch of the southern constellation of Fornax, the Hubble Ultra Deep Field (HUDF). Precise spectroscopic information was measured for ten times as many galaxies as have been detected in this field over the last decade by ground-based telescopes. The original HUDF images were pioneering deep-field observations with the NASA/ESA Hubble Space Telescope published in 2004. Now, despite the depth of the Hubble observations, MUSE has — among many other results — revealed 72 galaxies never seen before in this very tiny area of the sky. The MUSE data provides a new view of dim, very distant galaxies, seen near the beginning of the Universe. It has detected galaxies 100 times fainter than in previous surveys, adding to an already richly observed field and deepening our understanding of galaxies across the ages.

“With MUSE we discovered lots of extremely faint and small galaxies, in fact many more than were previously expected, and the combined ultraviolet radiation from these ultrafaint galaxies plays an important role in shaping the universe as we know it,” says MUSE programme scientist Lutz Wisotzki.

The survey unearthed 72 galaxies known as Lyman-alpha emitters that shine only in Lyman-alpha light, the brightest line emitted by hydrogen gas. Because MUSE disperses the light into its component colours these objects become apparent, but they remain invisible in deep direct images such as those from Hubble. Another major finding of this study was the systematic detection of luminous hydrogen halos around galaxies in the early Universe, giving astronomers a new and promising way to study how material flows in and out of early galaxies.

Many other potential applications of this dataset are explored in the series of papers, and they include studying the role of faint galaxies during cosmic reionisation (starting just 380 000 years after the Big Bang), galaxy merger rates when the Universe was young, galactic winds, star formation as well as mapping the motions of stars in the early Universe.

MUSE is an integral-field spectrograph in operation at the Very Large Telescope (VLT) of the European Southern Observatory (ESO). The overall lead of the project is at the Observatoire de Lyon (CRAL) and at ESO. MUSE covers the visible to near-infrared region and can simultaneously record thousands of spectra of entire regions on the sky and reconstruct images from this data. MUSE is one of the most successful and requested instruments at the VLT. The MUSE collaboration takes advantage of its Guaranteed Time Observing (GTO). AIP members of the MUSE-GTO team include Andreas Kelz, Josephine Kerutt, Davor Krajnović, Martin Roth, Rikke Saust, Kasper Schmidt, Ole Streicher, Matthias Steinmetz, Tanya Urrutia, Peter Weilbacher, and Lutz Wisotzki.

"Several people at AIP were involved at various levels in the now published studies. The spectroscopic survey was one of the prime reasons for building MUSE. The AIP contribution was crucial, from building the instrument, developing the data reduction pipeline, to the scientific work published in the papers,” concludes Davor Krajnović.

Full image caption: Colour image of the Hubble Ultra Deep Field region observed with the MUSE instrument on ESO’s Very Large Telescope. The picture only gives a very partial view of the MUSE data, which also provide a spectrum for each pixel in the picture.

Credit: ESO/MUSE HUDF collaboration

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

20 November 2017. Scientists from the Leibniz Institute for Astrophysics Potsdam (AIP) have joined an international research team to create one of the largest sets of galaxies in a computer genera...

The Universe is filled with an immeasurable number of galaxies that themselves are accumulations of billions of stars. Understanding how these 'islands in the universe’ formed and evolved and how they are distributed throughout the Universe is central to the field of Cosmology. Luckily, we now live in an era where both ground- and space-based telescopes are being designed to study the Universe out to unprecedented distances, peering back billions of years to when the Universe was an infant. But the interpretation of these data requires theoretical models. As such, astronomers generate model universes, where galaxies are simulated, which may act as a test bed for the assessment of theories. However, such virtual universes are computationally expensive, numerically challenging, and often lack the sheer number and details of the galaxies we observe.

Now, an international team led by Prof. Alexander Knebe from the Universidad Autónoma de Madrid and Prof. Francisco Prada from the Instituto de Astrofísica de Andalucía (bringing together experts from South America, the USA, Europe, and Australia) has created one of the largest publicly available virtual universes, known as the “MultiDark-Galaxies”. What is provided to the community are galaxy catalogues based upon three distinct models that all include the physical processes relevant for galaxy formation and evolution, conforming to and reproducing specific empirical observations.

All galaxy data and also data for the simulation itself is available via the database www.cosmosim.org, hosted at the Leibniz-Institut for Astrophysics Potsdam in Germany. A selected subset is also available at www.skiesanduniverses.org, hosted at NMSU in the US and the Instituto de Astrofísica de Ansalucía CSIC in Spain. The more than 100 million virtual galaxies per model cover a cosmological volume comparable to that probed by on-going and future observational campaigns. They therefore equip researchers in the field with an unparalleled opportunity to better understand existing observations and to even make predictions for upcoming missions. More information can be found in the accompanying paper that has just been accepted by MNRAS and can be found on the arXiv: 1710.08150

Visualization of the model galaxies. The left panel shows a slice of thickness 4.7 million light years through the whole simulation that itself has a side length of 4.8 billion light years. Each galaxy is represented by a yellow dot; the background indicates the underlying dark matter density. The right panel zooms into a smaller region. Here the dark matter haloes hosting the galaxies are visible as circles, colour-coded according to the projected density. Their sizes are scaled with their masses. Credit: Kristin Riebe/AIP

The CosmoSim database is a service by the Leibniz-Institute for Astrophysics Potsdam (AIP). It contains public data from cosmological simulations of different sizes and resolutions. The data can be accessed via a web interface and Virtual Observatory tools.

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

17 November 2017. The Alfred P. Sloan Foundation will award a $16 million grant for the next generation of the Sloan Digital Sky Survey (SDSS-V). The grant will kickstart a groundbreaking all-sky s...

The Leibniz Institute for Astrophysics Potsdam (AIP) is an associate member of SDSS with usage rights for researchers and graduate students. “AIP’s main engagement is in the APOGEE survey, which complements the RAVE survey led by AIP,” says Prof. Dr. Matthias Steinmetz, AIP’s lead scientist in the SDSS collaboration. “With these surveys we have been able to dissect the Milky Way Galaxy and thus gain new insights in its structure and formation history.”

In the tradition of previous Sloan Surveys, SDSS-V is committed to making its data publicly available in a format that is helpful to a broad range of users, from the youngest students to both amateur and professional astronomers.

The survey operates out of both Apache Point Observatory in New Mexico, home of the survey’s original 2.5-meter telescope, and Carnegie’s Las Campanas Observatory in Chile, where it uses Carnegie’s du Pont telescope. SDSS-V will make use of both optical and infrared spectroscopy, to observe not only in two hemispheres, but also at two wavelengths of light.

It will take advantage of the recently installed second APOGEE spectrograph on Carnegie’s du Pont telescope. Both it and its twin on Apache Point penetrate the dust in our Galaxy that confounds optical spectrographs to obtain high-resolution spectra for hundreds of stars at infrared wavelengths. In the optical wavelengths, the survey’s twin BOSS spectrographs can each obtain simultaneous spectra for 500 stars and quasars. What’s more, a newly envisioned pair of Integral Field Unit spectrographs can each obtain nearly 2,000 spectra contiguously across objects in the sky.

SDSS-V will consist of three projects, each mapping different components of the universe: The Milky Way Mapper, the Black Hole Mapper and the Local Volume Mapper. The first Mapper focuses on the formation of the Milky Way and its stars and planets. The second will study the formation, growth, and ultimate sizes of the supermassive black holes that lurk at the centers of galaxies. The Local Volume Mapper will create the first complete spectroscopic maps of the most-iconic nearby galaxies. “These projects will be very complementary to the 4MOST science, of which AIP is a lead,” adds Dr. Cristina Chiappini who represents the AIP in the Collaboration Council.

SDSS is managed by the astrophysical research consortium for the Participating Institutions of the SDSS Collaboration. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the participating institutions. The project’s fifth generation is building its consortium, but already has support from 18 institutions including the Leibniz Institute for Astrophysics Potsdam.

Image caption: This artist's impression shows a cutaway view of the parts of the Universe that SDSS-V will study. SDSS-V will study millions of stars to create a map of the entire Milky Way. Farther out, the survey will get the most detailed view yet of the largest nearby galaxies like Andromeda in the Northern hemisphere and the Large Magellanic Cloud in the Southern hemisphere. Even farther out, the survey will measure quasars, bright points of light powered by matter falling into giant black holes. Credit: Image by Robin Dienel/Carnegie Institution for Science/SDSS

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to explicitly emphasize the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.